Office Productivity

30) LibreOffice Portable
This fork of the OpenOffice.org suite allows you to create documents, spreadsheets, presentations, databases, drawings and more that are compatible with Microsoft Word and other office productivity software. Note that this is a larger portable application  382-582MB. Operating System: Windows.

31) AbiWord Portable
If you only need a word processor, AbiWord gives you a more lightweight alternative to a full office productivity suite. It's just 15 MB installed, and it supports Word, WordPerfect and OpenOffice.org file formats. Operating System: Windows.

32) X-OOo4Kids
OpenOffice.org for Kids offers a simplified version of OpenOffice.org designed to be used by those aged 7-12. The advantage of this version, even if you're not a kid, is that it loads and runs very quickly and requires very little space on your portable drive. Operating System: Windows.

Operating System

33) Damn Small Linux
Just 50MB, Damn Small Linux (DSL) was designed to boot from a USB drive or a business card CD. It's based in part on Debian code and includes applications like Firefox, XMMS, Ted, XPDF and a surprising number of others. Operating System: Linux.

PDF Reader

34) Sumatra PDF
This lightweight PDF reader requires just one file, so it's easy to run from a USB drive. It's very fast, thanks in part to a minimalist design with only the most necessary features. Operating System: Windows.

Personal Finance Manager

35) YAPBAM
Short for "Yet Another Bank Account Manager," YAPBAM is a simple financial management program that can run from a USB drive. Key features include import and export capabilities, budgeting, alerts and more. Operating System: Windows, Linux, OS X.

Screenwriting

36) Portable Celtx
Celtx makes it easier to format text so that it meets the standards for screenwriting submissions. This version runs from thumb drives and other portable devices. Operating System: Windows.

Security

37) TrueCrypt
Downloaded more than 14 million times, TrueCrypt can protect your entire hard drive or thumb drive. Check the documentation area of the website for information on how to use portable mode. Operating System: Windows.

39) Portable KeePass
KeePass stores all of your passwords in an encrypted database so that you only have to remember one master password. The portable version lets you take your passwords with you wherever you go. Operating System: Windows, Linux, OS X.